1. Field of the Invention
The present invention relates to a system for supplying ultra pure and contamination sensitive chemicals to production lines for forming semiconductors, fiber optics, or like components. More particularly, this invention relates to a system carrying pyrophoric chemicals which allows the production line to operate continuously, and without interruption.
2. Description of Related Art
The manufacture of semiconductors, fiber optics, and the like components, typically requires production lines with systems for supplying high purity processing chemicals to diffusion furnaces, either directly or in carrier gases. Processing chemicals are liquids which may be directly injected into the processing stations, or which may be carried to the processing stations in a carrier gas. Direct chemical injection may be from bulk supply tanks, or may be from smaller supply containers which will be periodically refilled by bulk supply tanks. When the chemicals are applied by means of carrier gases, the liquid chemicals will be contained in temperature-controlled ampules or work cylinders, called xe2x80x9cbubblersxe2x80x9d. A stream of an inert carrier gas, such as nitrogen, helium, or the like, is injected into the bubbler ampules. The inert carrier gas bubbles upwardly through the liquid chemical in the bubbler ampule and creates a chemical-saturated carrier gas atmosphere in the ampule in the space above the supply of liquid chemical contained therein. The chemically saturated carrier gas is continuously drawn out of the bubbler and transferred into the component processing station, such as a diffusion furnace, as noted above. Alternatively, chemical can also be dispensed from a bulk supply tank to a smaller working container, and then chemical is dispensed as a liquid from the working container to a vaporizer unit housed within the component processing station. This configuration is desirable for chemicals that do not vaporize or transport well when using a bubbler.
The processing lines depend on a continuous supply of the chemicals being delivered from the chemical source in order to operate properly and efficiently. If the supply of the processing chemicals is interrupted, the production line must be shut down, and the diffusion furnace must be placed in a xe2x80x9cidlexe2x80x9d mode. If the chemical ampules are depleted of processing chemicals, they must be removed from the production line and replaced with freshly filled ampules.
To avoid the necessity of removing a bubbler ampule from the production line, additional bulk chemical supply containers may be incorporated into the production line. When a single bulk supply container is used in the production line, it must be periodically refilled with processing chemicals. The line must be shut down while the bulk supply container is refilled. The line can be run for a longer time period due to the use of the bulk supply container, however, the line still must be periodically shut down when the bulk supply container is depleted. When two bulk supply containers are used, one is a fixed container and the other is a replaceable mobile container. The ampule is replenished with chemicals from the fixed bulk container, and the fixed bulk container is refilled with chemicals from the replaceable, or shuttle, bulk container. The fixed bulk container is typically positioned on a scale or connected to a load cell so that the volume of chemical in the fixed bulk container is continuously monitored. Signals are transmitted to the system microprocessor controller or xe2x80x9cjunction boxxe2x80x9d which are indicative of the volume of chemical remaining in the fixed bulk container. The microprocessor controller manages about 2 points of use. For each point of use, there are four level sensors, i.e., empty, low, high or overflow. The low or high corresponds to the xe2x80x9cstartxe2x80x9d and xe2x80x9cstopxe2x80x9d sensors which trigger the signal initiation to fill the ampule or the removal of the request. The empty or overflow (xe2x80x9coverfillxe2x80x9d) sensors are emergency sensors if the start and stop sensors fail. The supply voltage for the sensor circuit is about +24 volts. All level sensors connect to +24 volt when dry. A pressure switch generates a junction box alarm when there is not enough clean dry air (CDA) pressure. The electrical connections include main power and interface connections. Power is configured for 110 VAC or 230 VAC. A circuit breaker located where the main power is connected can be used to shut off all power to the unit. Twin fans act to cool the electronics area of the unit. A dispense request connector is used to interface with the process equipment, in addition to supplying status and alarm signals.
Typically, when the fixed bulk container is seen to be 75% full, the controller activates a chemical transfer valve system which transfers chemical from the shuttle bulk container to the fixed bulk container, and when the fixed bulk container has been refilled, the controller deactivates the chemical transfer valve system. Thus, the fixed bulk supply container will be refilled several times before the shuttle supply container must be refilled. When the shuttle bulk supply container has been substantially emptied, the shuttle container is removed from the production line and is refilled at an off-site chemical supply repository, which is typically far removed from the processing plant.
The use of fixed and shuttle bulk chemical supply containers has proven to be functionally operative, but it would be desirable to be able to provide an alternative replenishment system for the chemical ampules; and even more desirable to provide a chemical replenishment system with a controller microprocessor which can operate the system in alternative chemical replenishment modes, one having a fixed and a replaceable bulk chemical supply containers, and the other having two replaceable bulk chemical supply containers.
Transportation of ultra high purity or ultra sensitive chemicals within the production lines require additional safeguards. For that reason, pyrophoric chemicals capable of self-ignition when it is exposed to air, are rarely in production lines. Automatic liquid replacement or refill systems for liquids have been utilized in other industries where the purity requirements of the liquid are far less stringent, and where pyrophoric reactions and extreme air (oxygen and moisture) sensitivity are not commonly encountered. Moreover, these replacement systems have been based upon measuring the weight of the liquid in the working container at comparative points in time or by using a time filling sequence to ensure the proper volumetric quantity is delivered. None of the systems were designed to work with the stringent requirements needed for ultra high purity or contamination sensitive chemicals in the compound semiconductor industry, and where the systems must accommodate pyrophoric metalorganic chemicals with their need to minimize fire, and eliminate air contamination hazards.
Additionally, automatic chemical refill systems servicing a multiple number of temperature controllers and their bubblers from one central refill control system have suffered from the problem that when one temperature controller has experienced problems or malfunctions in the system, all of the refill lines have to be shutdown until the problem is corrected. In current practice, most chemical refill systems are capable of operating up to four temperature controllers concurrently to supply vapors to a corresponding number of deposition tools. Thus, a repair required of just one temperature controller in the refill system could cause all of the temperature controllers in the system to be shutdown.
The bubblers are held in liquid, temperature-controlled baths, and must be periodically replaced based on the usage of the ultra high purity pyrophoric metalorganic (PMO) source chemical. The amount of chemical used is a function of the degree of saturation of the hydrogen carrier gas carrying the PMO chemical to the metalorganic chemical vapor deposition (MOCVD) reactor and the quantity of carrier gas used. Typical carrier gases are nitrogen, argon, or helium, but the preferred gas for PMO CVD is ultra high purity hydrogen. Some typical chemicals utilized in bubblers are trimethylgallium (TMG), triethylgallium (TEG), trimethylaluminum (TMA) and dopant chemicals, such as dimethylzinc (DMZ) and diethylzinc (DEZ). When the chemical in the bubbler is depleted, the bubbler has to be removed from the temperature bath and refilled at a remote site.
In the typical compound semiconductor prior art process which requires use of fresh liquid pyrophoric metalorganic (PMO) chemicals, a replacement bubbler is inserted into the liquid temperature bath. This replacement of the chemical, however, requires physical removal of the depleted bubbler from the liquid temperature bath and requires the MOCVD machine to be shut down for a period of time while the change is being made. Normally the MOCVD machine""s reactor zone temperature is lowered during these periods of non-operation. Prior to recommencing use of the replenished chemical, both the bubbler and the machine""s reactor zone must be reheated to their standard operating temperatures. Routinely, test samples are next run through the process to ensure that the replenished chemical is not contaminated, and that it is otherwise acceptable for use in the process, prior to resuming the production operation. The total, liquid chemical replacement process can take from two to eight hours, depending upon the chemical involved and the end product being made by the MOCVD machine.
These problems are solved in the design of the present refill system by providing a modular automatic refill system where the liquid level sensors operate completely independent from each other to automatically refill the bubbler in its liquid temperature bath without removing the bubbler from the bath.
This invention relates generally to a system to automatically refill a liquid from a bulk container to a smaller receiving container without contamination. More specifically, it relates to a modular system providing fresh liquid pyrophoric metalorganic (PMO) chemicals through an automatic refill to a plurality of working cylinders (in their corresponding temperature controlled baths) that supply a vapor to a corresponding number of metalorganic chemical vapor deposition (MOCVD) machines. Source liquid chemical cylinders have been utilized in the compound semiconductor industry to supply chemicals directly or indirectly via carrier gases that are either partially or fully saturated with the particular PMO chemical as a function of the liquid chemical cylinder""s temperature and pressure and the rate of carrier gas flow through the cylinder. Various ultra-high purity liquid PMO chemicals, including those commonly called dopants, are required for this industry.
Additionally, in conventional MOCVD reactors, it is common practice to use a vacuum pump to remove residual PMO vapors from transfer lines, before removing a cylinder or bubbler, to replace it, or to inspect it. The use of a vacuum pump has several disadvantages:
A vacuum pump requires that a trap be used to condense and thereby remove volatile chemicals before they reach the pump, in order to avoid corrosion and decomposition of the chemicals with formation of deposits on the working surfaces and moving parts of the pump.
A vacuum pump generates heat, which can interfere with temperature control of the system.
A vacuum pump, and attendant parts, supports and trap, requires space in the working area.
A vacuum pump is an expensive piece of equipment, which requires regular maintenance. Its trap requires regular inspection, replacement of low-temperature coolant, and regular removal of and disposal of the condensed, hazardous PMO chemicals. In addition, the vacuum pump requires regular changes of its sump oil due to the build-up of PMO""s in the oil, in spite of the aforementioned trap, which is never 100% efficient.
The use of the venturi for the present invention is not only unique, but often overlooked. This is due to the fact that under normal conditions, the vacuum that can be generated by the venturi is not sufficient to evaluate all of the pyrophoric chemicals so one could safely open the system for a container exchange. Thus, based on theoretical calculations, this type of a system would not work. However, the present inventors have incorporated the use of the venturi with a dilution/purge routine that surprisingly allows for all of the chemical to be removed from the system. Thus, a safe container exchange is possible. This avoids the conventional use of vacuum pumps or other such expensive equipment to achieve the desired vacuum.
The disadvantages of using a vacuum pump are overcome in the present invention by the forementioned use of a venturi to remove residual PMO chemical vapors. The use of a venturi for the removal of residual PMO vapors has several advantages:
A venturi requires no moving parts for its operation, and therefore does not require a trap be installed to remove volatile chemicals before they reach the venturi. The volatile chemicals treated by the venturi in this invention are exhausted directly through the venturi and are combined for disposal with the normal exhaust from the MOCVD tool.
Use of an inert gas, such as nitrogen, to operate the venturi ensures that highly reactive chemical vapors will not decompose in chemical or exhaust lines and that these reactive vapors can be safely exhausted directly to an abatement system without first passing through a mechanical pump.
A venturi generates little or no heat, and therefore has no effect on the temperature control system of this invention.
A venturi requires very little space within the system""s cabinet. A venturi""s small size allows further efficiency by reducing the volume of gases contained in shorter lengths of connecting lines.
A venturi is a very simple device, is inexpensive to install, and requires little or no maintenance.
The present invention is directed to a chemical refill system which comprises: (a) at least one primary chemical reservoir; (b) at least one secondary chemical reservoir; (c) a distribution means for supplying gas to the chemical refill system; (d) a conduit for connecting the means for supplying gas, the primary chemical reservoir, and the secondary chemical reservoir; (e) at least one venturi comprising a gas inlet, a gas outlet and an exhaust gas outlet, the venturi being disposed between the distribution means for supplying gas and the primary and secondary reservoirs; and (f) at least one valve disposed about the exhaust outlet, wherein the valve prevents diffusion of oxygen or any contaminants into the system. Preferably, the primary chemical reservoir is a bulk chemical supply tank and the secondary chemical reservoir is an ampule and receives chemical from the primary chemical reservoir and delivers chemical to a means for applying the chemical. The conduit connects the chemical refill system to a means for applying the chemical and comprises a plurality of transfer lines and a plurality of valves.
One embodiment of the chemical refill system further comprises a volume sensor which is capable of monitoring the volume of chemicals remaining in the primary and secondary chemical reservoirs. The volume sensor is operable to monitor the volume of chemical in the primary and secondary chemical reservoirs using one or more sensors selected from the group consisting of: optical sensor, thermal conductance sensor, capacitance sensor, weight scale, sonic sensor, nitrogen back pressure sensor, electrostatic charge sensor, float assembly level sensor, or any combinations thereof. Preferably, the volume sensor is an optical sensor utilizing a glass rod encased in the primary and secondary chemical reservoirs or a thermal conductance sensor utilizing a thermistor encased in the primary and secondary chemical reservoirs.
Another embodiment of the chemical refill system further comprises a liquid temperature sensor in each of the primary and secondary chemical reservoirs. A further embodiment of the chemical refill system comprises a microprocessor controller means for selectively operating the chemical refill system. Preferably, the microprocessor controller means is a programmable logic controller. Also preferably, the microprocessor controller means further comprises a set of solenoid valves.
One embodiment of the chemical refill system comprises two primary chemical reservoirs and two secondary chemical reservoirs. The chemical refill system for this embodiment has a microprocessor controller means which selectively operates the system in a fixed/shuttle mode which mode involves the use of a fixed primary chemical reservoir and the use of a shuttle primary chemical reservoir, or in a shuttle/shuttle mode which mode involves the use of a plurality of shuttle primary chemical reservoirs.
In another embodiment of the present invention, the secondary chemical reservoir of the chemical refill system is not an ampule, rather it is located within the component processing station. This allows for direct delivery of chemical to the process tool and is advantageous with the use of chemicals that do not vaporize or transport well with a bubbler or ampule system.
The present invention is also directed to a process for transporting a chemical comprising the steps of: (a) using a chemical refill system according to the present invention, as set forth above, and further comprising a microprocessor controller means which comprises a plurality of independently operating microprocessor-controlled modules, with each module matched electrically to each primary chemical reservoir, and programmed to control the refilling operation of each corresponding primary chemical reservoir; (b) monitoring the volume of chemical within each corresponding primary chemical reservoir; wherein each independently operating microprocessor-controlled module may be removed from the microprocessor controller without interrupting the operation of the remaining microprocessor-controlled modules and their corresponding primary chemical reservoirs; (c) sensing an alarm condition from a volume sensor; and (d) refilling each corresponding primary reservoir or shutting down each corresponding automatic refill line. Each microprocessor-controlled modules, upon sensing a low level or low pressure alarm condition from said sensor in each corresponding primary chemical reservoir, will act synchronously to cease operation from each corresponding primary chemical reservoir.
Another embodiment of the invention further comprises at least two check valves, wherein the check valves control the conduit between each of the primary chemical reservoirs.
In a further embodiment of the invention, the chemical refill system transports pyrophoric chemicals. Preferably, the chemical refill system transports liquid pyrophoric metalorganic chemicals.